Existing methods of zero-gravity body restraint are used aboard the NASA Space Shuttle. These primarily consist of strap type foot restraints, seat belts and shoulder harnesses, and sleeping bag type sleep restraints. Foot restraints consist of fabric loops positioned conveniently on "floor" surfaces in front of equipment and storage "wall" surfaces. Foot loops are an easy and quick means of restraint; however, they do not hold the body in a proper zero-gravity posture relative to equipment surfaces and are thus adequate only for short-term usage. Foot loops also require the use of handholds to stabilize the body while forcing the feet into the straps. Belts and harnesses are commonly used in conjunction with various seats aboard the Shuttle. They provide positive contact with surfaces of couches, waste management equipment, and health maintenance equipment. Though useful for tasks where positive contact with a seat or floor surface is needed, seat belts and shoulder harnesses have three disadvantages: (1) they must be adjusted by each crew member, (2) they must always be used in conjunction with a reactive surface such as a seat or floor, and (3) they can obstruct upper body movement. The Shuttle sleep restraints are designed specifically for sleeping and are not appropriate for normal crew activities.
Additional body restraints were explored aboard the NASA Skylab missions of the early 1970's, as described in Dalton, Maynard C., "Experience Bulletin No. 10: Body Restraint Systems," Man-Machine Engineering Data Application of Skylab Experiments M487/M516, NASA, December 1974. Notable among these were a thigh restraint designed for use with a wardroom table and a foot restraint involving the use of cleated shoes. The thigh restraint consisted of an adjustable metal clamp that actively grasped the thighs between contact points at the front and back of the leg. Optimally, this restraint was used in concert with a strap type foot restraint. This system of restraints failed to position Skylab astronauts correctly in relation to the wardroom table. Moreover, the restraint required adjustment of the clamp mechanism with each use. Ultimately, astronauts rejected the intended means of use and improvised easier, more comfortable means of use of the restraint, though even improvised techniques of restraint with the thigh restraint were not comfortable for long-term usage. When positive long-term restraint was needed, the astronauts relied on a cleated shoe and gridded floor foot restraining system. This involved the use of cleated shoes that inserted and twisted into an open triangular grid structure "floor" surface providing positive contact between the astronaut's shoes and the floor. The main disadvantage of this restraint system was that astronauts wore sturdy cleated shoes at all times. Also, sometimes the cleats were difficult to lock and unlock to and from the floor grid.
A variety of restraint systems not intended for zero or microgravity use are also known in the art. For example, U.S. Pat. No. 2,976,914, issued Mar. 28, 1961 to Miller, discloses Velcro fasteners for floor cushions in an aircraft cabin. U.S. Pat. No. 3,165,168, issued Jan. 12, 1965 to Rose, discloses a boatswain's chair waist restraint. U.S. Pat. No. 4,235,182, issued Nov. 25, 1980 to Burger, discloses a chest, foot and hand restraint system for water skiing and windsurfing. U.S. Pat. No. 4,457,510, issued July 3, 1984 to Pertschuk, discloses the use of Velcro pads to hold the user's feet against a wall while exercising. U.S. Pat. No. 4,591,148, issued May 27, 1986 to Slater, discloses the use of Velcro pads with a clamp to hold the user's feet against a door while exercising. U.S. Pat. No. 4,637,629, issued Jan. 20, 1987 to Cummings, discloses a flexible torso restraint for aircraft crew members that allows body movement within a localized space.
Various seating devices of special configuration intended for use in a gravity environment are also known in the art. For example, protective seats for aircraft use are disclosed in U.S. Pat. Nos. 3,826,434, issued July 30, 1974 to Von Beckh and 4,359,200, issued Nov. 16, 1982 to Brevard et al. U.S. Pat. No. 3,669,493, issued June 13, 1972 discloses a chair having knee rests of the same general type as the commercially available Balans chair. All of these prior art structures are either unsuitable for use in a zero or microgravity environment or have significant disadvantages that make them less than a complete solution for body restraint in such an environment.
Overall, previous and existing restraints are overly dependent on active means of body attachment and adjustment. Sometimes they are cumbersome combinations of restraints such as foot straps and thigh restraints. At other times they require tedious manipulation of buckles, latches, and adjustment screws.